1. Field of the Invention
This invention relates to a method of recognizing an object. In addition, this invention relates to an apparatus for recognizing an object which can be mounted on a vehicle. Furthermore, this invention relates to a recording medium storing a computer program for recognizing an object.
2. Description of the Related Art
A known object recognition apparatus for a vehicle emits a forward wave beam such as a light beam or a millimeter wave beam from the body of the vehicle, and enables the forward wave beam to scan a given angular region in front of the body of the vehicle. In the case where an object exists in the given angular region, the forward wave beam encounters the object before being at least partially reflected thereby. A portion of the reflected wave beam returns to the apparatus as an echo wave beam. The apparatus detects and recognizes the object in response to the echo wave beam.
The known object recognition apparatus is used in a warning system for a vehicle which alarms when an obstacle such as a preceding vehicle exists in a given angular region in front of the present vehicle. The known object recognition apparatus is used also in a system for a vehicle which controls the speed of the vehicle to maintain a proper distance between the vehicle and a preceding vehicle.
Japanese patent application publication number 8-240660 discloses an on-vehicle apparatus for recognizing objects. The apparatus in Japanese application 8-240660 includes a distance sensor mounted on the present vehicle which detects the longitudinal-direction and transverse-direction distances to objects from the present vehicle. The distance sensor generates detection data having pieces representing distances to objects respectively. The distances to the objects mean positions of the objects relative to the present vehicle. In the apparatus of Japanese application 8-240660, pieces of detection data which correspond to object positions close to each other and in a first prescribed mutual-distance range are collected into a block having a block label. Generally, there are a plurality of blocks. Speeds relative to the present vehicle and corresponding to respective blocks are calculated. Blocks which correspond to positions in a second prescribed mutual-distance range, and which correspond to speeds in a preset speed-difference range are collected into a group having a group label. Finally, an object is recognized from detection data pieces representing a group.
Japanese patent application publication number 11-337636 discloses a rear monitoring system for a vehicle. In the system of Japanese application 11-337636, a rear sensor outputs a plurality of wave motions for detection from the rear of one""s own vehicle toward different regions, and captures the reflected waves in response to each of the wave motions. The location of a wave motion reflecting point in the rear of one""s own vehicle is detected, and an object in the rear of one""s own vehicle is discriminated by an object discriminating means on the basis of the continuity of information on the location of a wave motion reflecting point. Then, the relative speed of the object discriminated by the object discriminating means with respect to one""s own vehicle is computed by deciding means. On the basis of the relative speed, it is determined whether or not the object is an approaching object. When there are a plurality of discriminated objects at this time, the distance between the two objects is compared with a reference distance obtained by multiplying the speed of one""s own vehicle by a predetermined time. When the distance between the two objects is equal to or less than the reference distance, the two objects are decided to be the one and the same object. Thus, in this case, the two objects are recognized as a single object at the object discriminating means.
Japanese patent application publication number 9-15331 discloses an on-vehicle apparatus for detecting an object. The apparatus in Japanese application 9-15331 includes a distance sensor which detects a distance between its own vehicle and an object by transmission and reception of laser light. Output data from the distance sensor are developed by a coordinate development means on the X-Y coordinates for which the longitudinal direction from the own vehicle is taken as the Y axis and the lateral direction as the X axis. A cell forming means which provides a plurality of cells divided at prescribed intervals in the directions of the X and Y axes sets the developed data on the cells, and outputs the X-Y coordinates and the number of the data of each cell as cell information. Based on this information, an object discriminating means attaches the same label to the cells near to each other, and discriminates a plurality of cells as the same object. Then, a setting number of data being closer in the distance in the longitudinal direction are selected out of the cell data corresponding to the same object, and the longitudinal-direction distances corresponding to the selected data are averaged into a mean value. The mean value is used as an indication of the distance in the longitudinal direction from the own vehicle to the object.
U.S. Pat. No. 5,710,565 discloses an inter-vehicle distance control system which includes a laser scanning type distance sensor for moving a laser beam in a width-wise direction of a system vehicle to implement scanning and to determine relative positions and relative angles of objects within a forward detectable zone. A determination is made as to same lane probabilities that the objects exist in the same lane of a road as the system vehicle on the basis of a variable probability distribution and the relative positions and the relative angles of the objets. A target preceding vehicle is selected from the objects on the basis of the same lane probabilities. Information of the target preceding vehicle is used in controlling the speed of the system vehicle to keep constant the distance to the target preceding vehicle.
U.S. Pat. No. 5,574,463 discloses an obstacle recognition system for a vehicle which includes a radar device for emitting a wave beam into a given angular range outside a vehicle, and scanning the given angular range by the wave beam. The radar device detects a reflected wave beam. A recognizing device is operative for recognizing an obstacle with respect to the vehicle on the basis of the result of detection of the reflected wave beam by the radar device. In the recognizing device, a point recognizing section recognizes obstacles as points, and a uniting section is operative for uniting adjacent points among the points provided by the point recognizing section. The uniting section provides sets each having adjacent points. A line-segment recognizing section is operative for detecting a specific set or specific sets of adjacent points among the adjacent-point sets provided by the uniting section, and for recognizing every detected specific set as a line segment having a length only along a width direction of the vehicle. Every specific set has a length smaller than a given length along a longitudinal direction of the vehicle. A position estimating section estimates the position of a line segment, which will be provided by the line-segment recognizing section, in response to the position of a previously-provided line segment. An identity judging section is operative for comparing the line-segment position estimated by the position estimating section and the position of a line segment currently provided by the line-segment recognizing section to judge whether or not the line segment currently provided by the line-segment recognizing section and the previously-provided line segment are the same.
It is known to use target models in object recognition for a vehicle. In some cases, there simultaneously occur a correct target model and a wrong target model as a result of recognition concerning one object. The wrong target model is caused by, for example, noise. Generally, every target model has object information. An example of the object information includes a piece representing the center position of an object, a piece representing the size of the object, and a piece representing the speed of the object relative to the vehicle. When two target models become positionally coincident with each other, one of them is selected as an effective target model and the other is deleted. Thus, only the object information related to the selected target model continues to be effective. An example of conditions of the selection is as follows. Measurement is given of a first time interval during which a first target model is continuously detected, and a second time interval during which a second target model is continuously detected. In the case where the first and second target models become positionally coincident with each other, the first and second measured time intervals are compared with each other to decide which of them is longer (or which of them is shorter). Then, one of the first and second target models which corresponds to the longer measured time interval is selected as an effective target model. This selection is based on the idea that one of the first and second target models which corresponds to the longer measured time interval agrees with a correct target model while the other agrees with a wrong target model.
There is a chance that under certain circumstances, one of the first and second target models which corresponds to the shorter measured time interval agrees with a correct target model while the other agrees with a wrong target model. In these circumstances, the correct target model is deleted, and the wrong target model is selected. The deletion of the correct target model reduces the accuracy of object recognition.
It is a first object of this invention to provide a method of accurately recognizing an object.
It is a second object of this invention to provide an apparatus for accurately recognizing an object.
It is a third object of this invention to provide a recording medium storing a computer program for accurately recognizing an object.
A first aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of calculating positions of the objects; calculating a lane-sameness probability for each of the objects that the object and the subject vehicle are on a same lane; generating object information pieces corresponding to the objects respectively, the object information pieces representing the calculated positions of the objects and the calculated lane-sameness probabilities for the objects; determining whether or not at least two objects among the objects become substantially equal in position; in cases where it is determined that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; selecting one from the at least two objects which relates to a calculated lane-sameness probability equal to or higher than a predetermined value; and causing said single object to take over an object information piece corresponding to the selected object.
A second aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of calculating positions of the objects; determining whether or not a recognition state of each of the objects is stable; generating object information pieces corresponding to the objects respectively, the object information pieces representing the calculated positions of the objects and whether or not the recognition states of the objects are stable; determining whether or not at least two objects among the objects become substantially equal in position; in cases where it is determined that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; selecting one from the at least two objects whose recognition state is determined to be stable; and causing said single object to take over the object information piece corresponding to the selected object.
A third aspect of this invention provides a method of applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and recognizing objects located ahead of the subject vehicle on the basis of reflected waves which result from reflections of the transmission wave. The method comprises the steps of periodically calculating positions of the objects; estimating current positions of the objects on the basis of previously calculated positions thereof; calculating deviations between the estimated current positions of the objects and currently calculated positions thereof; generating object information pieces corresponding to the objects respectively, the object information pieces representing the calculated positions of the objects and the calculated deviations related to the objects; determining whether or not at least two objects among the objects become substantially equal in position; in cases where it is determined that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; selecting one from the at least two objects which relates to a smallest calculated deviation; and causing said single object to take over the object information piece corresponding to the selected object.
A fourth aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and detecting objects on the basis of reflected waves which result from reflections of the transmission wave; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means. The recognizing means comprises 1) first means for calculating positions of the recognized objects; 2) second means for calculating a lane-sameness probability for each of the recognized objects that the object and the subject vehicle are on a same lane; 3) third means for generating object information pieces corresponding to the recognized objects respectively, the object information pieces representing the calculated positions of the recognized objects and the calculated lane-sameness probabilities for the recognized objects; 4) fourth means for determining whether or not at least two objects among the recognized objects become substantially equal in position; 5) fifth means for, in cases where the fourth means determines that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; 6) sixth means for selecting one from the at least two objects which relates to a calculated lane-sameness probability equal to or higher than a predetermined value; and 7) seventh means for causing said single object to take over an object information piece corresponding to the object selected by the sixth means.
A fifth aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and detecting objects on the basis of reflected waves which result from reflections of the transmission wave; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means. The recognizing means comprises 1) first means for calculating positions of the recognized objects; 2) second means for determining whether or not a recognition state of each of the recognized objects is stable; 3) third means for generating object information pieces corresponding to the recognized objects respectively, the object information pieces representing the calculated positions of the recognized objects and whether or not the recognition states of the recognized objects are stable; 4) fourth means for determining whether or not at least two objects among the recognized objects become substantially equal in position; 5) fifth means for, in cases where the fourth means determines that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; 6) sixth means for selecting one from the at least two objects whose recognition state is determined to be stable; and 7) seventh means for causing said single object to take over the object information piece corresponding to the object selected by the sixth means.
A sixth aspect of this invention provides an object recognition apparatus comprising radar means for applying a transmission wave to a predetermined range in a width-wise direction of a subject vehicle, and detecting objects on the basis of reflected waves which result from reflections of the transmission wave; and recognizing means for recognizing objects located ahead of the subject vehicle on the basis of results of detection by the radar means. The recognizing means comprises 1) first means for periodically calculating positions of the recognized objects; 2) second means for estimating current positions of the recognized objects on the basis of previously calculated positions thereof; 3) third means for calculating deviations between the estimated current positions of the recognized objects and currently calculated positions thereof; 4) fourth means for generating object information pieces corresponding to the recognized objects respectively, the object information pieces representing the calculated positions of the recognized objects and the calculated deviations related to the recognized objects; 5) fifth means for determining whether or not at least two objects among the recognized objects become substantially equal in position; 6) sixth means for, in cases where the fifth means determines that at least two objects become substantially equal in position, recognizing the at least two objects as a single object; 7) seventh means for selecting one from the at least two objects which relates to a smallest calculated deviation; and 8) eighth means for causing said single object to take over the object information piece corresponding to the object selected by the seventh means.
A seventh aspect of this invention is based on the fourth aspect thereof, and provides an object recognition apparatus wherein the recognizing means further comprises eighth means for determining whether or not a recognition state of each of the recognized objects is stable; ninth means for adding results of the determining by the eighth means to the object information pieces; tenth means for, either in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities equal to or higher than the predetermined value or in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities less than the predetermined value, selecting one from the at least two objects whose recognition state is determined to be stable; and eleventh means for causing said single object to take over the object information piece corresponding to the object selected by the tenth means.
An eighth aspect of this invention is based on the fourth aspect thereof, and provides an object recognition apparatus wherein the recognizing means further comprises eighth means for estimating current positions of the recognized objects on the basis of previously calculated positions thereof; ninth means for calculating deviations between the estimated current positions of the recognized objects and currently calculated positions thereof; tenth means for adding the deviations calculated by the ninth means to the object information pieces; eleventh means for, either in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities equal to or higher than the predetermined value or in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities less than the predetermined value, selecting one from the at least two objects which relates to a smallest calculated deviation; and twelfth means for causing said single object to take over the object information piece corresponding to the object selected by the eleventh means.
A ninth aspect of this invention is based on the fourth aspect thereof, and provides an object recognition apparatus wherein the recognizing means further comprises eighth means for determining whether or not a recognition state of each of the recognized objects is stable; ninth means for adding results of the determining by the eighth means to the object information pieces; tenth means for estimating current positions of the recognized objects on the basis of previously calculated positions thereof; eleventh means for calculating deviations between the estimated current positions of the recognized objects and currently calculated positions thereof; twelfth means for adding the deviations calculated by the eleventh means to the object information pieces; thirteenth means for, either in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities equal to or higher than the predetermined value and only one of the at least two objects has a recognition state determined to be stable or in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities less than the predetermined value and only one of the at least two objects has a recognition state determined to be stable, selecting one from the at least two objects whose recognition state is determined to be stable; fourteenth means for causing said single object to take over the object information piece corresponding to the object selected by the thirteenth means; fifteenth means for, either in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities equal to or higher than the predetermined value and two or more of the at least two objects have recognition states determined to be stable or in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities less than the predetermined value and two or more of the at least two objects have recognition states determined to be stable, selecting one from the at least two objects which relates to a smallest calculated deviation; and sixteenth means for causing said single object to take over the object information piece corresponding to the object selected by the fifteenth means.
A tenth aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the recognizing means further comprises eighth means for estimating current positions of the recognized objects on the basis of previously calculated positions thereof; ninth means for calculating deviations between the estimated current positions of the recognized objects and currently calculated positions thereof; tenth means for adding the deviations calculated by the ninth means to the object information pieces; eleventh means for, either in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities equal to or higher than the predetermined value and two or more of the at least two objects have recognition states determined to be stable or in cases where a plurality of objects among the at least two objects relate to calculated lane-sameness probabilities less than the predetermined value and two or more of the at least two objects have recognition states determined to be stable, selecting one from the at least two objects which relates to a smallest calculated deviation; and twelfth means for causing said single object to take over the object information piece corresponding to the object selected by the eleventh means.
An eleventh aspect of this invention is based on the fifth aspect thereof, and provides an object recognition apparatus wherein the second means in the recognizing means comprises means for calculating an acceleration of each of the recognized objects relative to the subject vehicle, means for judging whether or not the calculated acceleration is in a predetermined range hardly occurring under usual traffic conditions, means for, when the calculated acceleration is judged to be in the predetermined range, determining that a recognition state of the related object is not stable, and means for, when the calculated acceleration is judged to be not in the predetermined range, determining that a recognition state of the related object is stable.
A twelfth aspect of this invention provides a recording medium storing a program for controlling a computer operating as the recognizing means in the object recognition apparatus of the fourth aspect of this invention.